This invention relates to noninvasive probes for monitoring the condition of a patient and to a system for sensing when the probe has become disconnected from the patient.
In various medical fields, it is common to have one or more probes that are attached to the skin of a patient. In most cases of real time monitoring, it is relatively easy for the user to determine when the probe has become disconnected from the patient as the signal being monitored generally will either be discontinued or be so unlike the anticipated signal that the user will immediately know that something is wrong. For example, when a EKG probe becomes disconnected from the patient, the loss of a signal becomes readily apparent and the user can take immediate action to reestablish the probe onto the patient.
In the case of infant warmers, however, as an example, generally temperature probes are connected to an infant and which monitor the temperature of that infant. The probe may simply monitor temperature or, as is common, the probe may be used as a feedback loop to control the energy to a heater to provide the amount of heat actually needed by the infant.
In such cases, however, the surrounding temperature may not be that different from the patient temperature so that a patient probe may become disconnected and the user may not see a rapid loss or deterioration of signal or other indication that would provide an early warning of the patient disconnect. Accordingly, the temperature probe for an infant may be disconnected and thus the control of the energy to the heater lost for a period of time that the user is simply unaware of the problem.
Examples of such a patient disconnect devices are shown and described in U.S. Pat. Nos. 4,399,823 and 4,399,824 of Air Shields, Inc., however, the similar systems therein described utilize a precise pulse of heat to the temperature responsive device and the accurate measurement of the dissipation of that heat to determine whether or not the probe is still attached to the patient. That system is somewhat expensive and may not respond as reliably as desired.
Accordingly, it would be advantageous to provide a rapid, yet inexpensive, indicator of a patient disconnect in the use of an infant warmer or other infant control apparatus, such as a incubator where temperature is being monitored and yet which is of sufficient reliability.